2.0 Functional Description
Fusion 878A
2.10 Video Data Format Conversion
PCI Video Decoder
2-30
Conexant
100600B
2.10.3 YCrCb to RGB Conversion
The 4:2:2 YCrCb data stream from the video decoder portion of the Fusion 878A
must be converted to 4:4:4 YCrCb before the RGB conversion occurs, using an
interpolation filter on the chroma data path. The even valid chroma data passes
through unmodified, while the odd data is generated by averaging adjacent even
data. The chroma component is up-sampled using the following equations:
For n = 0, 2, 4, etc.
Cb
n
= Cb
n
Cr
n
= Cr
n
Cb
n+1
= (Cb
n
+ Cb
n+2
)/2
Cr
n+1
= (Cr
n
+ Cr
n+2
)/2
RGB Conversion:
R = 1.164(Y–16) + 1.596(Cr–128)
G = 1.164(Y–16) – 0.813(Cr–128) – 0.391(Cb–128)
B = 1.164(Y–16) + 2.018(Cb–128)
Y range = [16,235]
Cr/Cb range = [16,240]
RGB range = [0,255]
2.10.4 Gamma Correction Removal
Fusion 878A provides gamma correction removal capability. The available
gamma values are:
NTSC: RGBout = RGBin
2.2
PAL: RGBout = RGBin
2.8
Gamma correction removal capability is not programmable on a field basis.
Furthermore, gamma correction removal is not available when YCrCb data is
output.
2.10.5 YCrCb Sub-sampling
The 4:2:2 data stream is horizontally sub-sampled to 4:1:1 using the following
equations:
For n = 0, 4, 8, etc.:
Cb
n
= (Cb
n
+ Cb
n+2
)
Cr
n
= (Cr
n
+ Cr
n+2
)
Vertical sub-sampling is supported by Fusion 878As YUV9 and YUV12
planar modes. In these modes, the video data is first planarized and placed in the
FIFO as 4:2:2 planar or 4:1:1 planar data. The FIFO data is then vertically
sub-sampled to 4:1:1 for YUV9 and 4:2:2 for YUV12 formats. The vertical
sub-sampling is performed via RISC instructions that are executed by the DMA
controller.
, shows an example of a 4-pixel line for YUV9 and YUV12 formats.
In the YUV12 format, line 2 of Cr/Cb data is discarded, and hence 4:2:2 vertical